Killer tarantulas with giant penises have been discovered in the Arabian Peninsula and Horn of Africa.

Researchers said they have identified four new tarantula species so distinct that they created a new genus named Satyrex.

The males are said to possess the longest palps ever recorded in tarantulas – reproductive appendages used during mating.

In Satyrex ferox, the largest species, the male palp measures an astonishing 5 cm, almost four times the length of the front part of its body, where the head and legs are attached.

The animal lives up to its name, which means 'fierce'.

Dr Alireza Zamani of the University of Turku, who led the study, said: 'This species is highly defensive. At the slightest disturbance, it raises its front legs in a threat posture and produces a loud hissing sound by rubbing specialised hairs on the basal segments of the front legs against each other.'

Scientists believe the extraordinary length of the male palps helps keep males at a safer distance during mating, avoiding attacks by highly aggressive females.

The new genus also includes species named after their regions - Satyrex arabicus and Satyrex somalicus - and a brightly coloured species, Satyrex speciosus.

All members of Satyrex live underground, digging burrows beneath shrubs or rocks.